Many toxins kill cells by the metabolic generation of chemically reactive intermediates that in turn produce alterations is cellular molecules, compromising cell structure and function, and leading to loss of viability. Many chemical and biochemical changes are observed in such studies, not all of which are involved critically in the mechanism of toxicity. Nevertheless, three major classes of tissue alteration are recognized, alkylation, peroxidation, and oxidation. A difficulty is be study of oxidant stress-induced cell death has been the lack of an animal model. Although the mechanistic involvement of reactive oxygen species has been proposed for tissue damage initiated by several drugs, by hyperoxic and by reflow following ischemia, much of what is known about the mechanisms through which reactive oxygen specials kill cells has been developed in studies conducted in vivo, particularly in isolated or cultured rat hepatocytes. We have found that diquat produces massive centrilobular hepatic necrosis with minimal mortality in male Fischer-344 rats and this model has been studied further in an effort to understand how reactive oxygen species and oxidant stress kills cells in vivo and to develop criteria for distinguishing those examples of cell death in vivo that are mediated by oxidant mechanisms from those that exert their lethal effects through other mechanisms. Investigations of the diquat model of reactive oxygen-mediated acute hepatic necrosis have demonstrated some important differences from reactive oxygen- mediated in vitro. Subsequent investigations of diquat-induced hepatic necrosis have revealed an apparently critical role of lipid peroxiation in the expression of reactive oxygen toxicity in vivo, and that the availability of chemically reactive chelates of iron is an essential determinant of lipid peroxidation and cell death initiated by reactive oxygen species (at least in the only in vivo model for necrosis this far established). The studies described in this proposal are designed to determine the extent to which lipid peroxidation is the cause of the defect in calcium regulation observed in association with diquat-induced hepatic necrosis and the manner in which chemically reactive iron chelates influence the course of these events. These investigations, therefore, are directed at major gaps in our understanding of oxidant stress- induced cell death and will provide a basis for understanding the relationship between major biochemical and chemical hypotheses of acute cell death.